Collapse repeated whitespace for normal and nowrap #902

Chromium collapses consecutive spaces in white-space: normal, but GPU-IX paints both spaces and can move later words to another line.

This reproduces on GPU-IX main (6b1eb39bf94c60af99379a1b94af4e9616bc461e):

<text style={{ width: 320, fontFamily: "Avenir Next", fontSize: 13, lineHeight: "16px", whiteSpace: "normal" }}>
  {"aa  bb"}
</text>

Chromium paints aa bb on one line. GPU-IX retains the two authored spaces and paints aa bb. In the final verification for PR #869, the same text at a narrow probe width produced aa / bb in Chromium and aa / b / b in GPU-IX. That run did not record the narrow probe's width.

GPU-IX sends the original text to GPUI's shape_text path without collapsing whitespace. Collapse runs of spaces and tabs to one space under normal and nowrap, convert newlines to spaces, and remove spaces at a wrapped line start. Keep the authored text available to accessibility and selection APIs.

Done means focused line-layout tests cover a fitting line, a break between words, and spaces at the start of a wrapped line; GPU-IX matches Chromium's visible text and line strings in each case.